Back to Saturn? Five Missions Proposed to Follow Cassini

Titan

As a spacecraft, Dragonfly would be an oddity: It would have propellers, like a helicopter — “a nuclear quadcopter to look for life on Saturn’s moon, Titan,” Peter Bedini, a program manager at Johns Hopkins Applied Physics Laboratory, said in a recent talk.

Proponents of this concept say a quadcopter would be an ideal way to explore Titan, Saturn’s largest moon. The air is thick there, thicker than on Earth. The landscape is varied, interspersed with obstacles — rivers, lakes and seas of liquid methane — that could prove inaccessible for a rover.

The booming popularity of flying drones in recent years makes the technology potentially feasible for interplanetary exploration, too.

“Ten years ago, they were kind of rare things that only enthusiasts experimented with,” said Elizabeth Turtle, a planetary scientist at the Johns Hopkins laboratory, who would serve as the mission’s principal investigator. “Now everyone can have a drone.”

In the past, scientists have suggested exploring the moon with balloons and airplanes. But Titan’s geology — sand dunes, eroded gullies — is more interesting than what is in the air. Dragonfly would fly from place to place, but would spend most of its time performing experiments on the ground.

“In terms of what we’re looking for on Saturn, it really hit exactly the sweet spot,” Dr. Turtle said.

A second Titan proposal, Oceanus, is led by Christophe Sotin, the chief scientist for solar system exploration at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., which was Cassini’s home base.

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The Oceanus spacecraft would study the moon from orbit, potentially identifying habitable regions for life.

Enceladus

Jonathan I. Lunine, a planetary scientist at Cornell University, was a member of the science team managing the Huygens probe, which traveled to Saturn with Cassini and landed on Titan.

He would be the principal investigator on a proposed mission to revisit Enceladus, a small moon just 313 miles wide. The discovery of geysers shooting from its south pole was a stunning surprise, and now the moon is considered a prime place for look for life.

“Cassini gave us a big pointer to where we need to go to look for life,” Dr. Lunine said. “If we are interested in trying to find life beyond the Earth, that’s the place we need to go, and we know how to do it.”

The proposed spacecraft, called Enceladus Life Finder, would fly through the plumes like Cassini did but with more sophisticated instruments capable of identifying a wide variety of molecules including amino acids, which would hint at signs of life.

NASA is also considering a second Enceladus mission concept called Enceladus Life Signatures and Habitability. That team, led by Christopher P. McKay, an astrobiologist at NASA Ames Research Center in Mountain View, Calif., has not talked in public about its proposal.

Saturn

The Saturn Probe Interior and Atmosphere Explorer would essentially do what Cassini did on Friday: descend into the planet’s atmosphere. But it would go much deeper.

The main part of the mission would end quickly — in about 90 minutes, as the probe parachuted into the atmosphere. It would take measurements of certain elements like helium that are hard to measure.